Add test case for empty dataset types upon database build

[kmdouglass]

Currently, there is no checking for empty dataset types (locResults, etc.) when the database is built. I need to handle the case when these might be empty, for example when no widefield images are present.

[kmdouglass]

Actually, this is not strictly true. locMetadata cannot be placed if no locResults exist.

Also, now that #13 is addressed, the user can check to see what will go into the database using the dryRun feature before the database is actually built. This allows the user to write their own checks for whether metadata, localization results, etc. are missing.